1. Field of the Invention
The present invention relates generally to an apparatus and method for allocating resources and performing communication in a communication system, and, in particular, to an apparatus and method for allocating resources and performing communication using them in a wireless communication system.
2. Description of the Related Art
Communication systems have been developed to enable exchange of voice and data between terminals located far away from each other. In addition, a wireless communication system provides voice or data services between terminals in a specific area using wireless resources. The wireless communication system uses various multiple access schemes in order to perform communication with a plurality of terminals. The multiple access schemes are classified, according to resources used, into Code Division Multiple Access (CDMA) that performs multiple access using code resources, Frequency Division Multiple Access (FDMA) that performs multiple access using frequency resources, and Time Division Multiple Access (TDMA) that performs multiple access using time resources.
Of the schemes, the CDMA scheme is most generally used. However, the CDMA scheme has difficulty in transmitting a large amount of data due to a limited amount of available orthogonal codes. Research is currently being conducted on many schemes of using alternative resources other than the orthogonal codes, and one of these schemes is the FDMA scheme.
The FDMA scheme includes not only an Orthogonal Frequency Division Multiplexing (OFDM) scheme that transmits data using multiple carriers, but also a Single-Carrier FDMA (SC-FDMA) scheme which is proposed as an uplink multiple access scheme in the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE).
In wireless communication, the high-speed, high-quality data service generally depends on the channel environment. In wireless communication, the channel environment is subject to frequent change due to a change in power of a received signal, caused by fading as well as Additive White Gaussian Noise (AWGN), shadowing, a Doppler effect caused by movement of a terminal and a frequent change in its velocity, interference from other users and multi-path signals, and the like.
Therefore, wireless communication needs to effectively cope with the foregoing issues in order to support the high-speed, high-quality data service. One of the typical transmission schemes and techniques used for overcoming channel fading in the general FDMA systems, such as OFDM and SC-FDMA, includes a frequency diversity technique. In the frequency diversity technique, if good and bad channels occur alternatively in a frequency domain, symbols in one data packet are transmitted over a broad band, thereby uniformly experiencing both the good and bad channels. In terms of reception performance, because modulation symbols included on one packet include both symbols experiencing bad channels and symbols experiencing good channels, the frequency diversity technique can demodulate the packet using the symbols experiencing good channels. The diversity technique is suitable for traffic susceptible to delay, such as the real-time traffic, or traffic that should not be applied only to the channel environment of a specific user, like the broadcast channel, the common control channel, and the like.
FIG. 1 illustrates exemplary unit resources allocable for transmitting data using a frequency diversity technique. In FIG. 1, reference numeral 110 indicates a subcarrier, which is a basic unit of the frequency domain, in an OFDM system, and indicates a unit frequency resource corresponding to the subcarrier in an SC-FDMA system, referred to herein as a subcarrier. During frequency diversity transmission, subcarriers constituting a unit resource should be uniformly located over the full band so as to efficiently obtain frequency diversity, but should not necessarily be limited to a specific pattern. For convenience, it is assumed herein that subcarriers in a unit resource are located at regular intervals. Particularly, in a Distributed FDMA (DFDMA) scheme that uses the diversity technique in uplink SC-FDMA, if subcarriers are located at regular intervals, a low Peak-to-Average Power Ratio (PAPR) is possible due to the single carrier characteristic. In addition, a unit resource composed of hatched subcarriers 120 is defined as a subcarrier set, and the number of allocable subcarrier sets is denoted by R 130 in FIG. 1. The parameter R is equal to an interval between consecutive subcarriers in one subcarrier set as shown by reference numeral 130. The subcarrier sets are independently defined according to an offset of an initial subcarrier, which is a unique value for each individual subcarrier set. For example, in FIG. 1, reference numeral 120 indicates a subcarrier set with an offset that equals zero. For each individual subcarrier set, the offset value can be used as resource allocation information.
As described above, the subcarrier set is a basic unit for resource allocation. Therefore, a base station can allocate more than two subcarrier sets to one terminal according to the amount of transmission data or channel condition. In this case, a method of selecting arbitrary subcarrier sets and independently signaling offset values is not an efficient signaling method. Therefore, in allocating resources to a terminal, it is preferable for the base station to allocate subcarrier sets with consecutive offset values. Efficient signaling methods include a 1-dimensional resource allocation signaling method (or 1-D signaling of resource allocation) and a tree-structured resource allocation signaling method.
FIG. 2 illustrates an exemplary method of allocating more than two subcarrier sets to one terminal. Referring to FIG. 2, reference numeral 210 shows frequency resources allocated to a specific terminal or User Equipment (UE), and reference numeral 220 means a parameter R for an interval of a subcarrier set allocable in frequency resources as described in FIG. 1. As illustrated, subcarrier sets allocated to a specific UE (or UE1) have offset values of 0 and 1, respectively. If subcarrier sets with consecutive offset values are simultaneously allocated in this manner, an effect that subcarriers used by the corresponding terminal are uniformly distributed in the frequency domain may decrease, thereby limiting performance gain due to frequency diversity. Particularly, in DFDMA transmission, because subcarriers allocated to one terminal are not located at regular intervals, the single carrier characteristic disappears, causing an increase in the PAPR.